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Chapter 3

Chapter 3. The Relational Database Model Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel. In this chapter, you will learn:. That the relational database model takes a logical view of data

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Chapter 3

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  1. Chapter 3 The Relational Database Model Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel

  2. In this chapter, you will learn: • That the relational database model takes a logical view of data • The relational model’s basic components are relations implemented through tables in a relational DBMS • How relations are organized in tables composed of rows (tuples) and columns (attributes) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  3. In this chapter, you will learn (continued): • About relational database operators, the data dictionary, and the system catalog • How data redundancy is handled in the relational database model • Why indexing is important Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  4. A Logical View of Data • Relational model • Enables programmer to view data logically rather than physically • Table • Has advantages of structural and data independence • Resembles a file from conceptual point of view • Easier to understand than its hierarchical and network database predecessors Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  5. Tables and Their Characteristics • Table: two-dimensional structure composed of rows and columns • Contains group of related entities = an entity set • Terms entity set and table are often used interchangeably Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  6. Tables and Their Characteristics (continued) • Table also called a relation because the relational model’s creator, Codd, used the term relation as a synonym for table • Think of a table as a persistent relation: • A relation whose contents can be permanently saved for future use Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  7. Tables and Their Characteristics (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  8. Tables and Their Characteristics (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  9. Keys • Consists of one or more attributes that determine other attributes • Primary key (PK) is an attribute (or a combination of attributes) that uniquely identifies any given entity (row) • Key’s role is based on determination • If you know the value of attribute A, you can look up (determine) the value of attribute B Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  10. Keys (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  11. Keys (continued) • Composite key • Composed of more than one attribute • Key attribute • Any attribute that is part of a key • Superkey • Any key that uniquely identifies each row • Candidate key • A superkey without redundancies Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  12. Keys (continued) • Nulls: • No data entry • Not permitted in primary key • Should be avoided in other attributes • Can represent • An unknown attribute value • A known, but missing, attribute value • A “not applicable” condition • Can create problems when functions such as COUNT, AVERAGE, and SUM are used • Can create logical problems when relational tables are linked Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  13. Keys (continued) • Controlled redundancy: • Makes the relational database work • Tables within the database share common attributes that enable the tables to be linked together • Multiple occurrences of values in a table are not redundant when they are required to make the relationship work • Redundancy exists only when there is unnecessary duplication of attribute values Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  14. Keys (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  15. Keys (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  16. Keys (continued) • Foreign key (FK) • An attribute whose values match primary key values in the related table • Referential integrity • FK contains a value that refers to an existing valid tuple (row) in another relation • Secondary key • Key used strictly for data retrieval purposes Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  17. Keys (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  18. Integrity Rules Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  19. Integrity Rules (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  20. Integrity Rules (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  21. Relational Database Operators • Relational algebra • Defines theoretical way of manipulating table contents using relational operators • Use of relational algebra operators on existing tables (relations) produces new relations Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  22. Relational Algebra Operators (continued) • UNION • INTERSECT • DIFFERENCE • PRODUCT • SELECT • PROJECT • JOIN • DIVIDE Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  23. Relational Algebra Operators (continued) • Union: • Combines all rows from two tables, excluding duplicate rows • Tables must have the same attribute characteristics • Intersect: • Yields only the rows that appear in both tables Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  24. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  25. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  26. Relational Algebra Operators (continued) • Difference • Yields all rows in one table not found in the other table — that is, it subtracts one table from the other • Product • Yields all possible pairs of rows from two tables • Also known as the Cartesian product Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  27. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  28. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  29. Relational Algebra Operators (continued) • Select • Yields values for all rows found in a table • Can be used to list either all row values or it can yield only those row values that match a specified criterion • Yields a horizontal subset of a table • Project • Yields all values for selected attributes • Yields a vertical subset of a table Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  30. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  31. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  32. Relational Algebra Operators (continued) • Join • Allows information to be combined from two or more tables • Real power behind the relational database, allowing the use of independent tables linked by common attributes Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  33. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  34. Relational Algebra Operators (continued) • Natural Join • Links tables by selecting only rows with common values in their common attribute(s) • Result of a three-stage process: • PRODUCT of the tables is created • SELECT is performed on Step 1 output to yield only the rows for which the AGENT_CODE values are equal • Common column(s) are called join column(s) • PROJECT is performed on Step 2 results to yield a single copy of each attribute, thereby eliminating duplicate columns Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  35. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  36. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  37. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  38. Relational Algebra Operators (continued) • Natural Join: • Final outcome yields table that • Does not include unmatched pairs • Provides only copies of matches • If no match is made between the table rows • the new table does not include the unmatched row Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  39. Relational Algebra Operators (continued) • Natural Join (continued): • The column on which the join was made - that is, AGENT_CODE - occurs only once in the new table • If the same AGENT_CODE were to occur several times in the AGENT table, • a customer would be listed for each match Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  40. Relational Algebra Operators (continued) • Equijoin • Links tables on the basis of an equality condition that compares specified columns of each table • Outcome does not eliminate duplicate columns • Condition or criterion to join tables must be explicitly defined • Takes its name from the equality comparison operator (=) used in the condition • Theta join • If any other comparison operator is used Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  41. Relational Algebra Operators (continued) • Outer join: • Matched pairs are retained and any unmatched values in other table are left null • In outer join for tables CUSTOMER and AGENT, two scenarios are possible: • Left outer join • Yields all rows in CUSTOMER table, including those that do not have a matching value in the AGENT table • Right outer join • Yields all rows in AGENT table, including those that do not have matching values in the CUSTOMER table Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  42. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  43. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  44. Relational Algebra Operators (continued) • DIVIDE requires the use of one single-column table and one two-column table Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  45. Relational Algebra Operators (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  46. The Data Dictionary and System Catalog • Data dictionary • Provides detailed accounting of all tables found within the user/designer-created database • Contains (at least) all the attribute names and characteristics for each table in the system • Contains metadata—data about data • Sometimes described as “the database designer’s database” because it records the design decisions about tables and their structures Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  47. A Sample Data Dictionary Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  48. The Data Dictionary and System Catalog (continued) • System catalog • Contains metadata • Detailed system data dictionary that describes all objects within the database • Terms “system catalog” and “data dictionary” are often used interchangeably • Can be queried just like any user/designer-created table Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  49. Relationships within the Relational Database • 1:M relationship • Relational modeling ideal • Should be the norm in any relational database design • 1:1 relationship • Should be rare in any relational database design • M:N relationships • Cannot be implemented as such in the relational model • M:N relationships can be changed into two 1:M relationships Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  50. The 1:M Relationship • Relational database norm • Found in any database environment Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

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